EP3129527A1

EP3129527A1 - Method for passivating a metal surface

Info

Publication number: EP3129527A1
Application number: EP15712058.5A
Authority: EP
Inventors: Michael Grabowski; Daniel BLUCHER; Michael Korte; Matthias Brettmann; Sannakaisa Virtanen
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 2014-04-11
Filing date: 2015-03-21
Publication date: 2017-02-15
Anticipated expiration: 2035-03-21
Also published as: CN106164343B; DE102014005444A1; CN106164343A; ES2747966T3; WO2015154851A1; US20170037517A1; EP3129527B1; US10351959B2

Abstract

The invention relates to a method for passivating a metal surface (25) of a light-weight metal part (3), wherein a conversion layer (5) is applied to the surface (25) of the light-weight metal part (3) in a passivation step (P). According to the invention, a passivation step (P) is carried out wherein an aqueous passivation solution is used to create a calcium phosphate-containing conversion layer (5) on the metal surface (25) of the part (3), said conversion layer (5) comprising oxides and hydroxides from the material of the part (3) and from the passivation solution and containing amino acids.

Description

Method for passivating a

metallic surface

The invention relates to a method for passivating a metallic surface of a light metal component according to the preamble of

Claim 1 and a passivation solution for forming a

Conversion layer for the metallic surface of the light metal component according to claim 15. The use of light metal components is industry-standard practice. Especially in vehicle construction, for example, vehicle bodies in mixed construction, for example, made of light metal and sheet steel parts to achieve a weight reduction. By way of example, aluminum or magnesium materials or alloys thereof can be used as the light metal.

From DE 196 30 289 C2 a generic method for painting vehicle bodies is known. Consequently, the body shell is subjected to pre-treatment before the actual painting process, in which bodies are first degreased in a spray and Volltauchzone. Subsequently, the cleaned vehicle bodies are coated in a phosphating bath with a zinc phosphate layer. This serves as additional corrosion protection and as a primer for the subsequent primer. Subsequent to this pretreatment step, a cataphoresis primer is applied in the dipping process, in which under-applied electrical DC voltage which are dissolved in the immersion paint particles are attracted to the body panel and adhere there to form a primer. Subsequently, the primed vehicle body is conveyed in a downstream continuous furnace in which the primer is baked. Subsequently, the provided with the primer vehicle body is led to another coating station in which a top coat is done in the desired color by the customer. In this case, the paint particles can be transported by an electrostatic field of high voltage standing support heads to the grounded body. This topcoat is also followed by a continuous furnace in which curing of the topcoat takes place at high temperature. Subsequently, a clearcoat is applied in a further coating station, which is also cured at high temperature in a subsequent drying step.

In vehicle bodies manufactured in mixed construction, the light metal components (made of Mg or Al) are more susceptible to corrosion than the steel components. Especially paint undercuts and filiform corrosion are more common damage patterns. To protect the light metal components, a pickling passivation and the application of an anodic coating is common practice. However, the commercial coatings only partially provide the necessary protective effect against self-corrosion, filiform corrosion and / or paint infiltration. Especially in contact with magnesium, the high potential difference should be regarded as promoting corrosion.

The commercially available coating systems for light metal components do not exhibit sufficient passivating behavior and are often too "noble" (ie too high a corrosion potential), especially with respect to magnesium more noble metals (for example, aluminum) electrochemically polarized, there is an exponential increase in the corrosion current.

The object of the invention is to provide a method for passivating the metallic surface of a light metal component, in which, in particular with aluminum or magnesium, a sufficient passivation is achieved and a contact corrosion risk is reduced.

The object is solved by the features of claim 1 or claim 15. Preferred embodiments of the invention are disclosed in the subclaims.

The invention is based on the idea of orienting the composition of the passivation solution, at least in principle, to the composition of human blood. Surprisingly, it has been found that certain components of human blood produce a protective and passivating coating on metal surfaces, especially of light metal such as aluminum and / or magnesium. In a specific embodiment of the invention, concentrations of individual constituents can be simulated essentially unchanged in the passivation solution. Against this background, according to the characterizing part of claim 1, a special Passivierungsschritt in which using an aqueous, especially blood-like passivation on the metallic component surface a calcium phosphate-containing conversion layer is generated, the oxides and hydroxides of the component material and the passivation solution and contains amino acids ,

The light metal component formed with the passivated metallic surface can be used across industries. exemplary The light metal component can be applied in the medical field. Alternatively, the light metal component may optionally be used in the automotive sector, and that is visible within the vehicle or as externally visible outer part. By way of example, the light metal component can be realized as a vehicle-inner-side display frame, an aggregate part, a chassis part or a component of a seat frame structure.

The passivating anticorrosive primer (ie the conversion layer) produces a reduction of the self-corrosive currents by a factor of 10. In addition, the pitting potential is increased by more than 0.5 V with a simultaneous reduction of the cathodic current densities. The conversion layer according to the invention is very favorably in contact with nobler materials (such as aluminum or steel). In addition, with the conversion layer according to the invention, there is a reduction in the contact corrosion currents with aluminum, steel, zinc, carbon fibers or CFRP. Furthermore, there is an increase in the penetration resistance by application of the coating (that is, the higher the penetration resistance, the lower the corrosion currents, the penetration resistance behaves inversely proportional to the corrosion currents). In addition, a passive behavior is generated in which much lower global corrosion currents occur. By comparison, in conventional conversion layers, a large number of finely divided local corrosion sites result. Overall, it should be emphasized that the conversion layer according to the invention generates low intrinsic corrosion currents and high passivity. In contact with aluminum and steel, only small contact corrosion currents result.

With a component material made of aluminum, the passivation solution results in a compact calcium phosphate and aluminum hydroxide / oxide-containing coating with amino acids. The layer morphology is constructed in the form of a lobe, with intermediate cracks which, for example, provide a sufficiently large residual conductivity in the case of a subsequent KTL deposition in a painting process. In addition, the liquid starting component of the primer can penetrate into the cracks, resulting in good adhesion between the conversion layer and the primer. °

Alternatively, in the case of a component material made of magnesium, a compact calcium phosphate and magnesium hydroxide / oxide-containing coating is obtained, the layer morphology of which is also formed in a lump-shaped manner.

In the following, further optional features of the invention are described: Thus, the passivation solution may preferably have at least the following constituents as activators for activating the metal surface of the component:

NaCl with a concentration between 5500 and 7500, in particular

6400 mg / l; and or

KCl with a concentration between 300 and 500, in particular

400 mg / l.

Both NaCl and KCl act as a source of chloride and assist in the activation of film formation which results in increased release of material ions from the surface of the device, which are necessary for film formation. In addition, the passivation solution may have at least the following amino acids as catalysts and layer formers:

D-Ca-pantothenate with a concentration between 2 and 5,

in particular 4 mg / l; and or

Myo-inositol with a concentration between 5 and 9,

in particular 7.2 mg / l, and / or L-isoleucine with a concentration between 80 and 120, in particular 105 mg / l.

The amino acid L-isoleucine acts specifically as a layering agent that supports the adhesion of the conversion layer on the metallic component surface.

In addition, Ca ²⁺ and / or P0 ₄ ^{3 "} ions are incorporated as fragments in the conversion layer to promote layer formation, in which case the passivation layer may preferably contain calcium phosphates.

In addition, the conversion layer may contain carbonaceous constituents. To provide such carbonate-containing layer constituents, the passivation solution may contain NaHCO ₃ . The carbonate formation is also dependent on possibly supplied C0 ₂ .

As a further adjuvant to promote layer formation, the passivating solution may contain Na pyruvate, with a concentration between 90 and 150 mg / l, in particular 110 mg / l. As stated above, an essential aspect of the invention is that certain components of human blood are transferred to the passivation solution in substantially unchanged concentrations. Accordingly, in one embodiment, the aqueous passivating solution may contain at least the following constituents, the concentrations of which are reproduced in their concentrations in human blood:

NaCl with in particular 6400 mg / l

KCl in particular 400 mg / l

NaH ₂ P0 ₄ with in particular 124 mg / l

CaCl ₂ with in particular 200 mg / l

NaHCQ ₃ with in particular 3700 mg / l Na pyruvate with in particular 110 mg / l

D-Ca-pantothenate with in particular 4 mg / l

Myo-inositol with in particular 7.2 mg / l

L-isoleucine with in particular 105 mg / l

Of essential importance for the coating behavior are at least one or more, in particular all of the following constituents

passivation:

L-arginine ^« HCI with in particular 84 mg / l

L-cystine with in particular 48 mg / l

L-histidine ^« HOH ₂ 0 with in particular 42 mg / l

L-leucine with in particular 105 mg / l

L-lysine HCI in particular 146 mg / l

L-methionine with in particular 30 mg / l

L-phenylalanine with in particular 66 mg / l

L-threonine with in particular 95 mg / l

L-tryptophan in particular 16 mg / l

L-tyrosine in particular 72 mg / l

L-valine in particular 94 mg / l

L-serine in particular 42 mg / l

Choline chloride in particular 4 mg / l

Folic acid in particular 4 mg / l

Nicotinamide with in particular 4 mg / l

PyridoxahHCI with in particular 4 mg / l

Riboflavin in particular 0.4 mg / l

Thiamine HCI in particular 4 mg / l

The passivation reaction according to the invention can be carried out at a pH of about 7. In this case, the coating reaction is slow. Alternatively, the coating reaction can also be in the acidic range occur. The coating reaction can be accelerated by increasing the temperature, - reducing the pH and / or by polarization and / or increasing the partial pressure of C0 ₂ . In a specific application, the light metal component may be a vehicle part, which is first pretreated with the passivation solution according to the invention to form the conversion layer. The conversion layer of the component can be covered with at least one further layer in a subsequent coating process.

By way of example, the coating process may comprise a first coating step in which a light metal KTL layer, ie an organic protective layer, is formed. This is done in a dipping process (ie light metal KTL) under applied DC voltage, whereby the paint particles dissolved in the immersion bath are attracted to the metallic component and remain there to form the light metal KTL layer. In a further coating step, a powder coating is then applied. This is done in a powder coating process with applied DC voltage. With regard to a process-reliable coating, the special clod-shaped layer morphology with the crack structures already mentioned above is of particular importance. This ensures namely in the dipping process and in the powder coating process sufficient electrical residual conductivity through the conversion layer. Subsequent to the component coating process, in one possible application the light metal component, for example as a visible outer part, can be joined in a riveting operation to the shell body not yet painted. The body shell is then subjected to a conventional body painting process together with the light metal component mounted thereon. That is, there is a cataphoresis primer of the body shell in immersion process, in which under applied electrical DC voltage dissolved in the immersion paint particles are attracted to the body shell and stick there to form a primer. Subsequently, the primed body shell is conveyed into a downstream continuous furnace, in which the primer is baked. Subsequently, the green body provided with the primer is led to another coating station in which a KTL process takes place. The KTL process is also followed by a continuous furnace in which the KTL layer burns in at high temperatures. Subsequently, in a further coating station, a conventional automotive paint system is applied, which is also baked in a subsequent drying step at high temperature.

In the above body painting process, the light metal component mounted on the green body is already precoated with a layer structure, namely with the conversion layer, the light metal KTL layer and the powder coating. The light metal component is thus electrically insulated, so that the electroplated in the bodyshell painting process KTL layer no longer adhere, while the conventional automotive paint system can be easily applied to the already coated light metal component.

The advantageous embodiments and / or developments of the invention explained above and / or reproduced in the subclaims can be used individually or else in any desired combination-except, for example, in the case of clear dependencies or incompatible alternatives.

The invention and its advantageous embodiments and further developments and advantages thereof are explained in more detail below with reference to drawings. Show it:

1 shows the layer structure of a finished painted light metal component, which is intended to represent here an example externally attachable to the vehicle body outer part.

Figs. 2 to 4 are respective flowcharts illustrating coating processes for producing the layer structure shown in Fig. 1; and

Fig. 5 to 7 respectively greatly enlarged partial sectional views, the

Illustrate the coating process until the application of the light metal KTL layer. In FIG. 1, the layer structure 1 of a paint coating on the metal surface 25 of a body component 3 is shown by way of example in a greatly enlarged partial sectional view. By way of example, here is the body part 3 made of light metal, such as aluminum, magnesium or an alloy thereof. Accordingly, the layer structure 1 directly on the workpiece surface 25 of the light metal component 3, a conversion layer 5, which serves for passivation and corrosion protection. The conversion layer 5 is coated by a light metal KTL layer 6. On this a powder coating 7 is formed, on which a conventional automotive paint system 9 is applied. As is further apparent from FIG. 1, the conversion layer 5 has a clod-shaped layer morphology, in which cracks 13 are formed between individual blocks 11. The cracks 13 provide in a KTL coating process described later for a sufficient residual conductivity between a cathodic dip bath and the light metal material of the component 3. In addition, during the multi-stage coating process, the liquid starting component of the light metal KTL layer 6 penetrate into the cracks 13 and thereby increase the adhesive bond to the conversion layer 5.

Fig. 1, as well as the other Figs. 2 to 7, are made with a view to a simpler understanding of the invention. Therefore, the figures are only roughly simplified representations that do not reflect a realistic layer structure 1. Thus, the conversion layer 5 actually has a layer thickness which lies in the μΐΎΐ range. 2 to 4, a series lacquer process carried out in a lacquering plant is described, in which a passivation solution according to the invention is used: Accordingly, a passivation step P (FIG. 2) first follows. In the passivation step P, a degreasing, grinding and / or pickling of the component 3 is performed. The thus cleaned component 3 is then subjected to a passivation according to the invention, in which it is immersed in an immersion bath of the passivation solution.

The composition of the aqueous passivating solution is basically based on the composition of human blood. Before this

In the background, the passivation solution contains at least the following

Main constituents whose concentrations are identical to those in human blood:

NaCl at 6400 mg / l

KCl with 400 mg / l

NaH ₂ P0 ₄ with 124 mg / l

CaCl ₂ at 200 mg / l

NaHCO ₃ with 3700 mg / l

Na pyruvate with 110 mg / l

D-Ca-pantothenate with 4 mg / l Myo-inositol at 7.2 mg / l

L-isoleucine at 105 mg / l

Here, NaCl and KCl in the passivation solution serve to activate the metal surface 25. The amino acids D-Ca-pantothenate and myo-inositol are mainly responsible for the coating process and also have a catalyzing effect. The components NaH ₂ P0 ₄ and CaCl ₂ support the coating process by incorporating the Ca ²⁺ and P0 ₄ ^{3 "} ions into the conversion layer 5.

The conversion layer 5 according to the invention also has carbonate-containing layer constituents. These are provided in the passivation solution by the component NaHC0 ₃ and C0 ₂ (from the atmosphere). Another component used for layer formation is the component Na pyruvate.

Of essential importance for the coating behavior are the following constituents of the passivation solution:

L-arginine ^« HCI mt 84 mg / l

L-cystine m t 48 mg / l

L-histidine ^« HCI-H ₂ 0 m 142 mg / l

L-leucine m 1 105 mg / l

L-lysine ^" HCI m 1 146 mg / l

L-methionine m 1 30 mg / l

L-phenylalanine m 1 66 mg / l

L-threonine m 1 95 mg / l

L-tryptophan m 1 16 mg / l

L-Tyrosine m t 72 mg / l

L-valine m t 94 mg / l

L-serine m 142 mg / l. The above amino acids are also components of human blood whose concentrations are almost unchanged.

Overall, therefore, the passivation solution according to the invention is an aqueous treatment liquid whose pH is in the range of about 7 or in the acidic range. The passivation takes place in the immersion bath at a treatment temperature in the range of 18 to 25 ° C. The treatment time depends on the set pH value, the process temperature and optionally an additional polarization as well as the required nominal thickness of the coating. After passivation, the component 3 is fed to a rinsing / drying process.

In the present application, the component 3 coated with the conversion layer 5 is provided in the further process sequence (according to FIG. 3) in a coating station 17 with a light metal KTL layer 6 (i.e., an organic protective layer). The light metal KTL is carried out in common practice in the dipping process in which an electrical DC voltage is applied between the body 1 and the dip tank, whereby the dissolved in the dipping bath paint particles are attracted to the component 3 and adhere there evenly. Additionally required pre- or post-treatment steps are omitted for the sake of easier understanding of the invention.

In a downstream drying station 18, the component 3 passes through a continuous furnace at a predetermined conveying speed, in which the light metal KTL layer 6 is baked at process temperatures in the range of, for example, 180 ° C. Subsequently, in process step II in a coating station 20, a powder coating is applied, in which the layer 7 (FIG. 1) is applied to the component 3. In the powder coating 20, the paint particles are under tension by an electrostatic field standing pointed heads transported to the grounded component 3. Subsequently, in a further drying station 19 again a baking process in a continuous furnace. Subsequent to the component coating process L (ie process steps I and II of FIG. 3), the light metal component 3 is joined in a riveting process to a shell body 15 which has not yet been painted, in an exemplary possible application as a visible vehicle exterior part. The green body 15 is conveyed in a continuous process in a body painting plant (see Fig. 4). There is a cataphoresis primer 25 in the dipping process in which under applied electrical DC voltage dissolved in the immersion paint particles are attracted to the body shell 15 and adhere there to form a primer. Subsequently, the primed shell body 15 is conveyed to a downstream continuous furnace 27, in which the primer is baked. Subsequently, the green body 15 provided with the primer is led to a further coating station 29, in which a KTL process takes place. The KTL process 29 is likewise followed by a continuous furnace 31, in which the coating is baked at high temperature. Subsequently, in a further coating station 33, a conventional automotive four-layer paint system 9 is applied, which is subsequently subjected to a baking process 35.

The body painting process shown in FIG. 4 is carried out with already pre-coated light metal component 3. That is to say that the light metal component 3 is electrically insulated, so that the cathodic electrocoating layer applied in the bodyshell painting process no longer adheres, whereas the conventional automobile paint system 9 (ie a four-layer structure) can be readily applied to the powder coating 7 of the light metal component 3. In FIGS. 5 to 7, the light metal component 3 is shown in different process steps in views corresponding to FIG. 1. Thus, in FIG. 5, the light metal component 3 with cleaned and exposed metallic surface 25 is shown. In Fig. 6 the light metal component 3 is shown after passivation and outsourcing. Accordingly, the conversion layer 5 is applied to the metallic surface 25 of the light metal component, namely with the Schollenmorphologie invention, ie with clod-like individual fragments 11 and intermediate cracks 13. In Fig. 7 is the light metal component 3 after the light metal KTL process shown, in which the starting component of the light metal KTL layer 6 soaks through the crack structure 13 of the conversion layer 5, whereby the adhesive bond between the conversion layer 5 and the light metal KTL layer 6 is substantially increased.

Claims

claims

Method for passivating a metallic surface (25) of a light metal component (3), in which a conversion layer (5) is applied to the surface (25) of the light metal component (3) in a passivation step (P), characterized in that in the passivation step (P ) using an aqueous passivation solution on the metallic component surface (25), a calcium phosphate-containing conversion layer (5) is produced, the oxides and hydroxides of the component material and the passivation solution and contains amino acids.

A method according to claim 1, characterized in that at least the metallic surface (25) of the component (3) by a light metal, in particular magnesium, aluminum or alloys thereof, is formed.

A method according to claim 1 or 2, characterized in that the passivation solution as activators for activating the metal surface (25) of the component (3) has at least the following constituents:

NaCl with a concentration between 5000 and 8000, in particular

6400 mg / l; and or

KCl with a concentration between 300 and 500, in particular 400 mg / l.

4. The method according to claim 1, 2 or 3, characterized in that the passivating solution comprises at least the following amino acids as catalysts and layer formers:

D-Ca-pantothenate with a concentration between 2 and 20,

in particular 4 mg / l; and or

Myo-inositol with a concentration between 2 and 20,

in particular 7.2 mg / l.

5. The method according to any one of the preceding claims, characterized in that the passivating solution has at least the following amino acid layer adhesion agent:

L-rlsoleucine with a concentration between 90 and 150, in particular 105 mg / l. 6. The method according to any one of the preceding claims, characterized in that the passivating solution to support the layer formation contains at least the following constituents, which are integrated as fragments (that is, Ca ²⁺ or P0 ₄ ^{3 "} ) in the conversion layer:

NaH ₂ P0 ₄ with a concentration between 100 and 170, in particular 124 mg / l, and / or

CaCl ₂ with a concentration between 170 and 300, in particular 200 mg / l. 7. The method according to any one of the preceding claims, characterized in that the conversion layer (5) for supporting the film formation has carbonate-containing constituents, and that in particular for the provision of the carbonate-containing constituents, the passivation solution contains NaHC0 ₃ , in particular with a concentration between 3500 and 4500 , in particular 3700 mg / l.

8. The method according to any one of the preceding claims, characterized in that the passivating solution to support the layer formation contains Na pyruvate, and that its concentration is between 90 - 170 mg / l, in particular at 10 mg / l.

9. The method according to any one of the preceding claims, characterized in that the pH of the passivation solution is in a neutral to acidic range.

10. The method according to any one of the preceding claims, characterized in that the aqueous passivation solution contains at least the following constituents, the concentrations of which are reproduced in their concentrations in human blood:

NaCl with in particular 6400 mg / l

KCl in particular 400 mg / l

NaH ₂ P0 ₄ with in particular 124 mg / l

CaCl ₂ with in particular 200 mg / l

NaHCO 3 with in particular 3700 mg / l

Na pyruvate with in particular 110 mg / l

D-Ca-pantothenate with in particular 4 mg / l

Myo-inositol with in particular 7.2 mg / l

11. The method according to any one of the preceding claims, characterized in that the passivation solution for increasing the coating behavior at least one or more, in particular all of the following constituents:

L-arginine ^» HCI with 50 to 120, in particular 84 mg / l

L-cystine at 30 to 80, especially 48 mg / l L-histidine ^" HOH ₂ 0 m 1 25 to 65, in particular 42 mg / l

L-leucine m 1 70 to 140, in particular 105 mg / l

L-LysirrHCI m 1 110 to 170, in particular 146 mg / l

L-methionine m 1 20 to 50, in particular 30 mg / l

L-phenylalanine with 40 to 80, in particular 66 mg / l

L-threonine with 60 to 120, especially 95 mg / l

L-tryptophan with 13 to 20, especially 16 mg / l

L-tyrosine with 40 to 90, especially 72 mg / l

L-valine with 60 to 120, especially 94 mg / l

L-serine with 20 to 60, in particular 42 mg / l

Choline chloride with 2 to 10, especially 4 mg / l

Folic acid with 2 to 10, in particular 4 mg / l

Nicotinamide with 2 to 10, especially 4 mg / l

Pyridoxal ^« HCl with 2 to 10, in particular 4 mg / l

Riboflavin with 0.2 to 1, in particular 0.4 mg / l

Thiamine HCl with 2 to 10, in particular 4 mg / l

2. The method according to any one of the preceding claims, characterized in that the conversion layer (5) of the component (3) in a subsequent coating process (L) with at least one layer (6, 7, 9) is covered.

3. The method according to claim 12, characterized in that the coating process (L) comprises a first coating step (I), in which a light metal KTL layer (6), ie an organic protective layer is formed, in particular in a dipping process under applied DC voltage, whereby the paint particles dissolved in the immersion bath are attracted to the metallic component (3) and adhere there to form the light metal KTL layer (6), and / or with at least one further coating step (II), in which at least one layer (7) is applied, in particular in a powder coating process with applied DC voltage. 14. The method according to any one of the preceding claims, characterized in that the conversion layer (5) is formed with a clod-shaped layer morphology (11) with crack structures (13), and that in particular the layer morphology (11) in the first coating step (I) a sufficient electrical Restleitfähigkeit between the dip and the component material ensures and / or by penetration of the liquid starting component of the light metal KTL layer (6) an adhesive bond between the conversion layer (5) and the light metal KTL layer (6) increases.

Passivation solution for forming a conversion layer (5) for a metallic surface (25) of a light metal component (3) in a method according to one of the preceding claims.